1. Field of the Invention
The present invention generally relates to a semiconductor device and a method of forming the same. More particularly, the present invention relates to a thin film transistor and a method of forming the same.
2. Description of Related Art
A thin film transistor (TFT) typically includes a gate, a gate insulating layer, a channel layer, a source/drain, and is usually used as a switching device in displays such as liquid crystal displays (LCDs). Usually, the TFT is formed by sequentially forming a gate, a gate insulating layer, an α-Si channel layer and a source/drain on a substrate. The gate is made of a single metal layer of aluminium (Al), chromium (Cr), tungsten (W), tantalum (Ta) or titanium (Ti), or made of multiple metal layers.
However, when a single-layer of the above-mentioned metal is used to form the gate, the surface of the layer can be easily eroded and reacts with oxygen in the atmosphere to form metal oxide, such that the subsequent etch process cannot be performed effectively. On the other hand, when the gate is made of multiple metal layers, such as molybdenum (Mo)/Al/Mo, oxidation and erosion can be prevented, but the process for forming multiple metal layers is surely more complex because more than one sputtering targets or deposition chambers are required. Moreover, the above problems also arise in the process for forming the source/drain.